228 Guide Bracket.
shaped to dimensions, leaving sufficient excess of width to allow
of accurate fitting to the Radius Link, after which it is case-
hardened and polished.
XIII. Guide Bracket for Valve Rods (Fig. 243).—The
machining is shewn on the drawing at A. Set the bracket
vertical by trial with square as at B, and line out the base a.
Scribe also the line b all round the casting, and at the proper
height from a. Lay level on its side as at c; find by
measurement the height of the boss and that of the foot centre.
Scribe the thickness of boss. Next shape to these lines as at D,
the boss with a front tool and the foot with a side tool. It
should be noted here that a side tool ought never to be used if it
can be avoided, for there is a great twisting action thereby pro-
duced which is calculated to wrench the tool from its box; but a
good deal is sometimes sacrificed to save two settings on the
machine. Re-scribe the line b from the marks left on the side of
the boss, and lay the bracket on its side as at p, packing until the
centres are level; then scribe the heights of the large holes on
both faces and strike the circles. The casting being hollow, the
core-hole must be spanned as-at G, in order to strike the bolt-
holes, whose centres are found by scribing a horizontal line and
squaring a vertical one when in the position c, and then bisecting
the right angles obtained. The bolt-holes are drilled as at H, but
the large holes are bored in the lathe, the bracket being clamped
to the face plate, and the latter provided with a balance weight.
This will be understood from B, where the face plate will be seen
dotted, and the bracket clamped in position for boring b. In all
such cases it is necessary to first drill a hole large enough to
admit the boring tool.
The Bushes are bored in a chuck, and finished on a mandrel,
and afterwards driven into the bracket, a block of wood being
placed upon them* to receive the blow of the hammer;
The oilcup cover is drilled for the hinge-pin, and finished by
hand, and the oil-holes drilled, and countersunk slightly at the
top. An £" spiral channelj/^hpuld be chipped in each bush with
round-nosed chiseLto.,allow the oil to flow.
XIV. Eccentric Sheave and Straps (Fig, 244).—The
castriron sheave will be taken first It is of the solid, form, being